New palaeomagnetic data from the Mahabaleshwar Plateau, Deccan Flood Basalt Province, India: implications for the volcanostratigraphic architecture of continental flood basalt provinces

Abstract

New magnetostratigraphic data from seven Western Ghats sections in the Deccan Volcanic Province are presented. These are combined with an established geochemically defined stratigraphy, and volcanological logs, to provide a correlated, chronological eruptive framework. We identify two magnetic polarities in five of the sections, and these are assigned to chrons 29r and 29n. Importantly, the reversal boundary represents an identifiable isochronous surface within the volcanic pile. This surface occurs at different elevations, as does the altitude of the geochemically defined formation boundary (i.e. Ambenali–Mahabaleshwar Fms), which defines a second isochronous surface. Inspection reveals significant differences in the number and thickness of lava units preserved between these two surfaces. This indicates that there was significant local topography ( c . 80 m) across Deccan Volcanic Province lava fields during their development; an interpretation consistent with topographies observed across modern and historical examples (e.g. Hawaii, Iceland). These data also indicate that the geochemical stratigraphies of continental flood basalt provinces can mask local and sub-regional detail in lava stacking patterns when applied at smaller spatial scales (<10 2 –10 4 m). Finally, transitional (R–N) directions preserved in some eruptive units place constraints upon the rates of eruption, and indicate c . 2 ka periods of volcanic repose.

Emplacement characteristics, time scales, and volcanic gas release rates of continental flood basalt eruptions on Earth

“…Evidence of hiatuses between the eruptions is presented by weathered surfaces on tops of lava fl ow fi elds, such as the red boles of the Deccan Traps (Widdowson et al, 1997), but we must remember that fl ow fi elds, per se, cannot be recognized in many continental fl ood basalt provinces, where only subvertical sections through the lavas are exposed. Diffi culties in correlating individual lava fl ows between outcrops (e.g., Jay et al, 2009) presently preclude the recognition of the geographic extent of single fl ow fi elds in provinces such as the Deccan Traps.…”

“…Assumptions about typical fl ow thicknesses can also give us insights into potential fl ow volumes. For the Deccan example, if areas from 70,000 to 175,000 km 2 were covered by pāhoehoe lava fl ow fi elds during emplacement of some formations in the Wai Subgroup (Self et al, , 2008a, then adopting a range of fl ow-fi eld thicknesses from 30 to 50 m (Jay et al, 2009) indicates eruptive volumes in the range 2100-8750 km 3 . Further, the Mesozoic to Cenozoic continental fl ood basalt provinces are the best studied and preserved, and the information is biased toward the younger examples.…”

Investigations related to scientific deep drilling to study reservoir-triggered earthquakes at Koyna, India

“…AGGM data covering 5,012 line km were recorded along N-S flight paths at an average 120-m drape surface, cutting across the Koyna seismic zone. The initial model is based on earlier geophysical information such as deep seismic sounding (Kaila et al 1981), deep resistivity sounding (Kailasam et al 1976), palaeomagnetic studies (Jay et al 2009), exploratory drilling (Roy et al 2013a, b) as well as MT sounding carried out recently (Patro et al pers. comm.).…”

Emplacement of inflated Pāhoehoe flows in the Naude’s Nek Pass, Lesotho remnant, Karoo continental flood basalt province: use of flow-lobe tumuli in understanding flood basalt emplacement

“…Bryan et al 2010;Self et al 2015), in thick packages spread over areas frequently in excess of a 1 × 10 6 km 2 (Self et al 2015), with very short time spans of emplacement (~1 Ma; Bryan et al 2010). They present challenges to understanding the sources of their magmas, temporal and spatial relationship to supercontinents (Svensen et al 2017), continental rifting and possible mantle plumes (Burke and Torsvik 2004;Ernst and Bleeker 2010), magma supply and distribution systems such as dyke and sill complexes, and not least lava flow emplacement and lava pile construction (Walker 1971;Jay et al 2009). The latter is important and raises a number of questions.…”